It is proposed to conduct systematic kinetic studies of thiosulfate reductase (EC unassigned) and 3-mercaptopyruvate sulfurtransferase (EC 2.8.1.2) with alternate substrates and inhibitors in an effort to define the biochemical roles of these activities in sulfane metabolism more precisely. Similarly, it is proposed to examine the binding of sulfur by serum albumin to characterize the carrier sites, particularly with respect to the relationships between sulfane metabolism and the known mechanisms of metabolism of other material. Finally, it is proposed to pursue investigation of the iron-sulfur protein xanthine oxidase to define the role of sulfane sulfur in its activity - especially to distinguish whether there is a direct catalytic role or, alternatively, the activity effects are secondary results of a primarily structural role.